The chief objective of the proposed research is to learn more about the development of the vertebrate germ line. In particular, it is hoped that new information will be gained about the factors which control the transition from a primordial to a mitotic to a meiotic stage of development. To examine these questions, lesions will be introduced by drug and hormonal treatment at specific stages of germ cell development in amphibians. Changes produced in development will be characterized by electron microscopy, autoradiography, in situ cytological and filter RNA-DNA hybridization, and direct biochemical isolation of nucleic acids and proteins. The experimental manipulation of germ cell development should also define the degree of relationship that exists between chromosomal DNA synthesis and extrachromosomal ribosomal DNA amplification. Density gradient techniques will also be employed as a means of obtaining purified germ cell populations for in vitro studies of RNA and protein synthetic activities. BIBLIOGRAPHIC REFERENCES: Kalt, M. R., H. Pinney and K. Graves. 1975. Inhibitor induced alterations in germ line cells of Xenopus laevis. Cell Tiss. Res. 161, 193-210. Kalt, M. R. 1976. Morphology and kinetics of spermatogenesis in Xenopus laevis of spermatogenesis in Xenopus laevis. J. Exptl. Zool., in press.